@Maurizio Giuffredi,Thanks for posting in Q&A.
From your description, I know you have deployed a Screen Lock policy, but it did not work as expect.
To narrow down this issue, please do some checks below.
1.Please be sure your computers meet the Device Lock CSP requirement.
2.Please check the policy status in Intune portal and whether the device applied the policy.
- You can check the Event log: Applications and Services Logs – Microsoft – Windows – Devicemanagement-Enterprise-Diagnostics-Provider – Admin and look for Event ID 813
- Check the reg key: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\PolicyManager\current\device\DeviceLock MaxInactivityTImeDeviceLock
3.Please check whether there exist Local Group Policy in targeted device. GPO takes precedence over Intune policy.
- Run RSOP to see if any GPO settings on the device affect this
If there is any unclear, feel free to let me know.
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.